You can drag and drop a single channel shader onto the item, (each shading domain will highlight in red)
or,..
In the shader tab (list) you can drag a single shader, and drop it into a shader channel, then drag and drop that icon onto the next channel down until they’re all the same.

NOTE: If the shader is texture based,. then depending on the model, and the way it’s been mapped, applying the same texture to al pats may not produce what you expect.